1. Field of the Invention:
The present invention relates to a radar guidance system and more particularly to an airborne radar system for guiding an airborne missile or the like to a ground target.
2. Description of the Prior Art:
Many air-to-ground missile guidance systems have been designed with various degrees of guidance accuracies. If the target to which a missile is to be directed is strong from a radiation reflection point of view, the problems of guiding a missile thereto are simple. System complexity greately increases with increased guidance accuracy and particularly in a system which is designed to guide a missile to a relatively weak target which can only be distinguished from radar returns of adjacent patches of ground by a trained operator. System complexity is further increased if the system is designed to direct the missile to a target from an aircraft which flies at a safe stand-off distance from the target.
Herebefore a radar ground mapping technology has been developed with which a history of the changes in range and azimuth of each element of ground of a selected resolution with respect to a flying aircraft is obtained, so that the various elements can be displayed to form a map of the ground. The map is updated at intervals which depend on the speed of the system. Such a mapping technique is referred to as a synthetic array radar mapping technique. With such a system the range and doppler frequency of any target of interest can be easily determined. The range is generally represented by a time delay from a time point of reference and the target azimuth is generally related to the doppler frequency shift.
Herebefore the range of a missile to a target could be controlled as it flies toward the target until the two are equal. However prior to the instant invention the target's doppler frequency shift or simply doppler frequency which is related to the target's azimuth could not be used to guide the missile in azimuth since the missile's frequency due to its velocity changes continuously and therefore could not be usefully made to equal the frequency of the ground target which is assumed to be stationary. Clearly a system capable of using the target's range and doppler frequency to guide a missile thereto would represent a significant advance in the art.